1. Field of the Invention
This invention relates to a web or sheet article wherein the article is encoded with information that controls operations performed on or with the article.
2. Prior Art
In the manufacture and/or use or of webs or sheets of material, it is important that certain manufacturing operations be accurately performed along the web length. A novel technique for web control is disclosed in copending U.S. patent Ser. No. 166,500 entitled "Continuous Web Registration", Hershey Lerner and Bernard Lerner, inventors, concurrently filed herewith. That application is incorporated herein by reference. According to the invention disclosed in that application a series of marks which emit visible or invisible electromagnetic wavelength-shifted radiation under an incident electromagnetic radiation are affixed to a web. The emitted radiation is of a different wavelength than the incident radiation and can be detected by a detector. Control circuitry coupled to the detector generates signals which can be used to control web manufacture and/or use.
Not all wavelength shifting materials are suitable for practice of the above invention. There have been proposals to use visible light detectors in conjunction with control marks which absorb ultraviolet light and emit visible light on articles other than webs. As an example, one proposal was to place a visible light emitting mark on a tube which, when detected by a visible light detector, was used to assist in rotational registration of the tube for sealing. The material that was used, however, emits visible light only in the presence of high energy ultraviolet light with a wavelength of about 2540 angstroms. Such high energy radiation can be damaging to the eye and therefore not suitable for use as a mark unless safety precautions are taken.
Other materials which emit visible light in response to less energetic electromagnetic energy are not suitable because they migrate through plastic. If control circuitry is to accurately determine a mark's position on a moving web, it is imperative that the material comprising the mark not bleed or migrate through the web surface so as to enlarge the mark. Migration may also cause a mark to flow through one layer of plastic web to another producing a mark where none was intended.
Although many materials which emit visible light radiation are known, the prior art does not teach any electromagnetic wavelength-shifting material for controlling the use and/or the manufacture of plastic webs, much less which materials would be especially suitable. Since electromagnetic wavelength-shifting control marks have never been affixed to plastic webs the problems that wavelength-shifting marks exhibit when used on plastic foils have never been recognized. Thus, there have been no successful proposals for marking a plastic sheet or web with materials that are readily detectable, i.e., that emit a visible or an invisible electromagnetic wavelength-shifted control signal, in response to non-harmful incident electromagnetic radiation, and remained in a fixed location on the web.